In recent years, as recording media of information, optical disks named as a “CD” and a “DVD” have been developed for commercial use. For writing or reading information with respect to these optical disks, the optical disks are irradiated with laser rays, and the writing of information is performed by the irradiated laser rays, while the reading of information is performed by the reflected laser rays reflected from the optical disks.
The laser rays are generated and emitted by the laser-diode provided at the pickup, and the laser-rays reflected from the optical disk is received by a photo-diode likewise provided at the pickup. The pickup is disposed slidably in the radial direction of the optical disk.
The relationship between the optical disk and the pickup will now be described with reference to FIG. 8. FIG. 8 is a side view showing the configuration of the pickup unit in a conventional optical-disk recording or reproducing device.
In this pickup unit 101 of the conventional optical-disk recording or reproducing device, a spindle motor 103 is fixed to one end portion on the top surface of a chassis 102. A turntable 104 is affixed on the rotating shaft 103a of the spindle motor 103. On the top surface of the turntable 104, an optical disk 105 is placed and rotated by the rotational driving of the spindle motor 103.
A field motor 106 is affixed on the bottom surface of the chassis 102, and the rotating shaft of the field motor 106 extends up to the top surface of the chassis 102 through an opening (not shown) provided in the chassis 102. At the end portion of the rotating shaft, a motor gear 106a is affixed. A first large-diameter gear 107a is in mesh with this motor gear 106a, and a first small-diameter gear 107b is provided coaxially with the first large-diameter gear 107a. Also, a second large-gear 107c is in mesh with this first small-diameter gear 107b, and a second small-diameter gear 107d is provided coaxially with the second large-diameter gear 107c. Each of the above-described gears is rotatably affixed to the chassis 102.
On the top surface of the chassis 102, a rack with which the second small-diameter gear 107d is in mesh as a pinion gear, is formed at one side portion of the chassis 102, and a plate gear 108 which slidingly moves straightly according to the rotation of the second small-diameter gear 107d is provided. A pickup 109 is affixed at the one side portion opposite to the one side portion where the rack of plate gear 108 is provided. This pickup 109 is arranged to be slidably secured by a pair of guide shafts 110 provided in parallel with the plate gear 108 (in FIG. 8, one guide shaft 110 alone is shown). The pickup 109 is affixed to the plate gear 108 so that the laser-ray emitting optical axis and the laser-ray receiving optical axis form a predetermined angle with respect to the information recording surface of the optical disk 105.
Here, the rotational driving of the field motor 106 is transmitted from the motor gear 106a to the first large and small diameter gears 107a and 107b, and the second large and small diameter gears 107c and 107d, and the plate gear 108 moves in the horizontal direction in the figure by the rotation of the second small diameter gear 107d. Thereby, the pickup 109 affixed to the plate gear 108 slidingly moves in the horizontal direction in the figure under the guide of the guide shaft 110. That is, the pickup 109 slidingly moves from the initial position of information recording on the inner peripheral side of the optical disk 105 toward the outer peripheral side thereof up to the position 109′ indicated by the dotted lines in the figure.
At this time, the distance between the optical disk 105 and the pickup 109 must be maintained at a predetermined dimension. Specifically, the demension of the distance “h1” between the bottom surface (in the figure) of the optical disk 105 and the top surface (in the figure) of the pickup 109 when the pickup 109 is situated at the initial position on the inner peripheral side of the optical disk 105, and the demension of the distance “h2” between the optical disk 105 and the pickup 109 when the optical pickup has moved up to the position 109′ corresponding to the edge portion on the outer peripheral side of the optical disk 105, must be kept at the same value (i.e., h1=h2).
For this purpose, the guide shaft 110 is arranged so that the end portions thereof are held so as to be adjusted by a guide shaft fixing member 111a and a guide shaft holding member 111b. More specifically, the guide shaft fixing member 111a fixes the guide shaft 110 at a standard guide shaft position, while the guide shaft holding member 111b has an elastic member and an adjusting screw each for adjusting the position of the guide shaft 110 in the vertical direction in the figure.
The configuration of this guide shaft holding member 111b will be described with reference to FIGS. 9 to 11. FIG. 9 is a developed perspective view showing the conventional guide shaft holding member, FIG. 10 is a sectional view thereof, and FIG. 11 is a view explaining the problem associated with the conventional guide shaft holding member.
The guide shaft holding member 111b comprises a bearing stand 121, an elastic member 124, an adjusting screw support plate 125, and an adjusting screw 127. In one side surface of the bearing stand 121, there is formed a shaft holding groove 122 in which the guide shaft 110 is to be inserted from the top surface (in the figure) and to be held. This shaft holding groove 122 in the bearing stand 121 comprises an opening which has a diameter slightly larger than that of the guide shaft 110, and a substantially tubular space portion 123 described later into which the elastic member 124 and the adjusting screw 127 are to be inserted. Also, screw holes 121a and 121b, which are described later, for affixing the adjusting screw support plate 125 are provided on the top surface of the bearing stand 121.
The elastic member 124, which is a helical spring, is fitted and inserted into the space portion 123 in the shaft holding groove 122 of the bearing stand 121. An end portion of the guide shaft 110 is inserted into the holding groove 122 of the bearing stand 121 from the shaft holding groove 122, and is placed on the top surface of the elastic member 124.
The adjusting screw support plate 125 is a planar metallic material having a shape and a size to be placed on the top surface of the bearing stand 121. On a substantially central portion of this adjusting screw support plate 125, a female screw hole 126 is provided at the position corresponding to the space portion 123 in the bearing stand 121. Also, screw through-holes 125a and 125b are formed at the positions corresponding to the screw holes 121a and 121b in the bearing stand 121, and thereby the adjusting screw support plate 125 is fixed to the bearing stand 121 by screws 128a and 128b. 
The adjusting screw 127 constitutes a male screw to be engaged with the female screw hole 126 in the adjusting screw support plate 125. After the elastic member 124 and the guide shaft 110 have been inserted into the shaft holding groove 122 in the bearing stand 121, the adjusting screw support plate 125 is secured by the screws 128a and 128b, and the adjusting screw 127 is engaged with the female screw hole 127 in the adjusting screw support plate 125. Then, by pressing the guide shaft 110 by the front end of the adjusting screw 127 against the elastic force of the elastic member 124, the position of the guide shaft 110 is adjusted.
Such a guide shaft holding member 111b is arranged so that the center of the guide shaft 110 and that of the adjusting screw 127 correspond with each other (see FIG. 10). As the adjusting screw 127, a ready-made screw is generally used. In general, therefore, the front end of the adjusting screw 127 which is in contact with the guide shaft 110 is only cut in a planar form without being subject to an accurate plane machining, so that the front end thereof includes unevenness and tilt to some extent. In order to smoothly perform the adjustment, the width of the shaft holding groove 122 is formed slightly larger than the diameter of the guide shaft 110, allowing for manufacturing errors. If the width of the shaft holding groove 122 is smaller than the diameter of the guide shaft 110, the guide shaft 110 will be inserted into the shaft holding groove 122 with pressure, thereby causing the dysfunction of the elastic force of the elastic member 124. As a result, the position of the guide shaft 110 will vary when subjected to vibration.
On the other hand, when a positional adjustment is to be performed by rotating the adjusting screw 127 and moving the guide shaft 110 in the vertical direction in the figure against the elastic force of the elastic member 124, it is desirable to be able to linearly adjust the height “h” with respect to the rotational pitch “t” of the adjusting screw 127 as indicated by the dotted line in FIG. 11. However, since the front end of the adjusting screw 127 which is in contact with the guide shaft 110, for example, has tilt as described above, the moving amount of the height becomes non-linear with respect to the rotational pitch “t” of the adjusting screw 127 as indicated by the solid line in FIG. 11, so that an accurate and fine positional adjustment of the guide shaft 110 becomes difficult. Moreover, since there exists a gap between the shaft holding groove 122 and the guide shaft 110, the guide shaft 110 undergoes the force of the adjusting screw 127 in the rotational direction by the rotation thereof and thereby moved within the shaft holding groove 122 in the horizontal direction in the figure. As a consequence, similarly, a fine adjustment of the guide shaft 110 becomes difficult.
As described above, the pickup 109 is provided with another guide shaft besides the illustrated guide shaft 110. This other guide shaft is disposed on the opposite side of the guide shaft 110 shown in FIG. 8 (i.e., on the rear side of the plane of the figure), and is engaged with the guide hole or the guide groove on the rear side of the plane of the figure showing the pickup 109. Both ends of this other guide shaft are held by guide shaft holding members each having an adjusting function for the guide shaft position similar to the guide shaft holding member 111b, thereby achieving an adjustment of the relative position with respect to the optical disk on the rear side of the plane of the figure showing the pickup 109.
As described above, the conventional positional adjustment of the pickup with respect to the optical disk is performed by means of the guide shaft holding members having the function of positional adjustment for the guide shaft, and provided at one end or both ends of each of the guide shafts for the pickup. In summary, the guide shaft holding member comprises a bearing stand having a shaft holding groove into which the guide shaft is inserted, an elastic member and an adjusting screw each disposed within this holding groove. The guide shaft holding member clamps the guide shaft between the elastic member and the adjusting screw, and performs a positional adjustment of the guide shaft by the rotational pitch of the adjusting screw.
However, since the surface of the adjusting screw which is in contact with the guide shaft has a configuration including unevenness and tilt, the movements of the guide shaft becomes irregular ones corresponding to the front end configuration of the adjusting screw, so that it is difficult to perform a guide shaft position adjustment in proportion to the rotational pitch of the adjusting screw. This has raised a problem that the optimum position setting for the guide shaft is very hard.
With a view to solving these problems caused by the conventional guide shaft position adjusting device, the object of the present invention is to provide an optical-disk pickup guide shaft adjusting device capable of a high-degree of adjustment, by causing guide shaft holding members having the position adjusting function by adjusting screws and elastic members provided at one end or both ends of the guide shaft, to have a construction allowing a linear positional adjustment of the guide shaft with respect to the rotational pitch of the adjusting screw.